YT does add significance to the overall "popularity" of the video. So, just because he copies you and you're first, you're not going to automatically beat him for being 'first' (its not like a duplicate content penalty on Google or something especially since to get his video uploaded YT has to see it as unique from other videos so its really not duplicate content anyways). If he has more ratings or thumbs up/views/comments, etc. that will do the trick. Also, he can have less activity total, like less views and thumbs up and comments, but if his video is a lot newer than yours so he's getting them at a faster rate (like your video has 100 thumbs up ratings but its been around a year and his has only 20 but his video is just a few days old) YT may still see it as being more "popular". As mentioned before it could also quite easily by the mentioned unlisted method (this is actually very likely because if he copied your exact title and description its likely he knows what he's doing and specifically targeting the search term you're ranking for and sees you at the top there and is trying to outrank you).
Its hard to say for certain because you just gave a little info and we're not looking at it. Could be a few different things take a look at his video and compare it to yours and think about it and you should be able to come up with at least an idea of what happened (and if not its probably the 'unlisted' method and the biggest sign of this is he's going to have considerably more views than you think he'd have for a video as new as it is).